Bryan Chung had a tutorial still available on the Internet Archive on how to connect a LED Matrix to an Arduino using a MAX7219:
Here is an experiment with an 8×8 LED
matrix, driven by a MAX7219 IC,
controlled through an Arduino
micro-controller board. A custom PCB
has been made by Tan from DinoTech to
tidy up all the wires connecting the
LED matrix and the IC. It comes with a
separate 12V power supply, in order
not to drain everything from the
Arduino board.
Only 4 wires are necessary to control
the MAX7219 driver IC. They are the
Data Clock Latch/load Ground
The data and clock pins should match
those for the shiftOut() command in
Arduino. The latch pin will give a LOW
to HIGH pulse after the shiftOut
command. I have written the original
program for Javelin Stamp. Since
Arduino can only shift 8 bits of data,
I have to use 2 separate commands to
shift both the upper and lower bytes
to the MAX7219, which needs a 2 bytes
control for each command.
For the data structure of the 8×8 LED
matrix, I use a byte array – matrix of
length 8. Each row in the matrix
corresponds to the Y dimension. Each
bit in a row corresponds to the X
dimension. Digit 1 is on; 0 is off.
The X direction is reversed and there
is also an 1 bit shift. The
updateLED() function caters for this.
The first program is an animation of a
single line motion.
int CLOCK = 12;
int LATCH = 13;
int DATA = 11;
byte matrix[8];
int idx = 0;
void setup() {
pinMode(CLOCK, OUTPUT);
pinMode(LATCH, OUTPUT);
pinMode(DATA, OUTPUT);
digitalWrite(CLOCK, LOW);
digitalWrite(LATCH, LOW);
digitalWrite(DATA, LOW);
initLED();
clearLED();
}
void loop() {
for (int j=0;j<8;j++) {
updateLED(idx, j, true);
}
refreshLED();
delay(200);
for (int j=0;j<8;j++) {
updateLED(idx, j, false);
}
refreshLED();
delay(100);
idx++;
idx %= 8;
}
void ledOut(int n) {
digitalWrite(LATCH, LOW);
shiftOut(DATA, CLOCK, MSBFIRST, (n>>8));
shiftOut(DATA, CLOCK, MSBFIRST, (n));
digitalWrite(LATCH, HIGH);
delay(1);
digitalWrite(LATCH, LOW);
}
void initLED() {
ledOut(0x0B07);
ledOut(0x0A0C);
ledOut(0x0900);
ledOut(0x0C01);
}
void clearLED() {
for (int i=0;i<8;i++) {
matrix[i] = 0x00;
}
refreshLED();
}
void refreshLED() {
int n1, n2, n3;
for (int i=0;i<8;i++) {
n1 = i+1;
n2 = matrix[i];
n3 = (n1<<8)+n2;
ledOut(n3);
}
}
void updateLED(int i, int j, boolean b) {
int t = 1;
int n = 0;
int m = 0;
if (j==0) {
m = 7;
}
else {
m = j-1;
}
n = t<<m;
if (b) {
matrix[i] = n | matrix[i];
}
else {
n = ~n;
matrix[i] = n & matrix[i];
}
}
